Wireless communications systems, such as Personal Access Communications Systems (PACS), require mobile communications made or received by a mobile user to be routed to the mobile user's terminal (the subscriber unit or mobile terminal) with little or no interruption in the call, even as the mobile user travels through one or more wireless communications coverage areas (CAs).
FIG. 1A illustrates a typical PACS 100. The PACS includes a switched telephone network 102, such as a public switched telephone network (PSTN) or an Integrated Signaling Digital Network (ISDN), connected to a wireless communications system 104. Also connected to the switched telephone network are a network database 106 and a network server 108. The network database 106 may be a Bellcore proprietary Advanced Intelligent Network service control point (SCP). The database 106 includes a Home Location Register (HLR) 110. The HLR 110 contains a database maintained by a user's local telephone company at the user's home location and includes information about the user called the user profile. The database 106 is connected to a network server or intelligent peripheral 108, such as a Bellcore Proprietary Intelligent Services Peripheral (ISP). The network server may include an access manager (AM) 109 which contains information about servicing the user's incoming and outgoing communications. The database 106 and server 108 preferably communicate using the 1129+ protocol, but any suitable communication protocol may be used.
The database 106 is connected to a Switching Transfer Point (STP) 111 in the switched telephone network 102. The STP 111 may be connected to a number of Service Switching Points (SSP) 112. The SSPs 112 connect to customer premises to provide for premises equipment, such as a wireline telephone 114. An SSP 112 may also be connected to one or more Radio Port Control Units (RPCU) 116, which are part of the wireless communications system 104. The RPCU 116 is connected to a number of Radio Ports (RP) (or Base Stations (BS)) 118, which monitor a "cell" (or "coverage area") 120. The RP (or BS) 118 and connected RPCU 116 are referred to herein collectively as a "radio system" (RS) 122. One RS 122 is shown in FIG. 1A in dashed lines. One or more RPCU 116 are connected to a second database called the Visiting Location Register (VLR) 124. The VLR 124 is maintained by a local telephone company at the location the mobile user and subscriber unit (or mobile terminal) 126 are visiting. The VLR 124 stores a subset of the HLR user information, and records that the subscriber unit (SU) 126 is currently located in that VLR. The HLR 110 keeps a record of the VLR in which the mobile terminal is currently registered. One VLR 124 may cover a number of RSs 122.
As seen in FIG. 1A, where a subscriber unit 126 initiates or receives a communication, it communicates with an RP (or BS) 118 using an air interface protocol. The RP 118 is connected to a RPCU 116 which communicates with an SSP 112 using an RS/switch protocol. The communication path between the SU 126 and another party on a wireline telephone 114 is shown with the thick arrow.
As seen in FIG. 1B, when the SU 126 travels to a new RS 122 (e.g., changes to RPCU 116'), as shown by arrow 128, communication is directed to the new RS 122'. The old RS hands over the call to the new RS and the registration information is updated in order for communications to be directed to the SU at its new location.
The switch 112 transfers the SU registration information and provides it to the new RPCU 116'. The location of the new RS is stored in the VLR 124. If the SU 126 travels to an RS 122 covered by another VLR 124, the switch 112 transfers the subset of the HLR data stored in the previous VLR to the new VLR. The location of the new VLR is stored in the HLR and the previous VLR location is deleted from the HLR 110. The updated registration and SU status information may also be stored in the AM 109.
In many known wireless communications system, such as the European GSM system and cellular telephone networks, when an SU moves from a first RS 122 to a second RS (such as illustrated by the arrow in FIG. 1B) during a call, the switch 112 performs the handover to the new RS. That is, the switch 112 handles the signaling used to make and break communications between the SU 126, the old and new RPs 118, and the switched telephone network 102.
If the handover is between RSs, the switch 112 handles the signaling used to switch the communications and information between old and new RPCUs 116. As seen in FIG. 1C, the call and all information related to it are transferred to switch 112' connected to the new RS. The new RS communicates with the SU using the air interface protocol and communicates with the switched telephone network using the RS/switch protocol. The communication path is shown with the thick arrow. This handover is undesirable because the switch is part of the switched telephone network 102 and has limited resources to process handovers. Handovers used a great deal of processing, particularly if the handover is between RSs. Thus, it is "expensive" (in terms of switch resources and bandwidth) to use the switch to perform the handover. Also, call maintenance information about service features--three way calling, call waiting, etc.--are maintained at the switch 112. This information is sent to the switch connected to the new RPCU. This, too, is an "expensive" use of network resources. Moreover, sending call maintenance information between switches incurs costly modifications to the software of the existing switches.
Therefore, it is an object of the present invention to provide a method for removing the handover control from the telephone network switch.
It is another object of the present invention to provide a method for keeping call maintenance information about service features in a single location during a wireless communication.
It is yet another object of the present invention to provide a method for maintaining a single interface between the wireless communication network and the switched telephone network during a call, even if the subscriber unit travels to different coverage areas during the call.
It is yet another object of the present invention to minimize the modification of the existing switches to accommodate the handovers.